The present invention relates to a method for processing manure, liquid manure and/or Kjeldahl-N containing waste water, being subjected to a nitrification in a first step and to denitrification in a subsequent step. An aerated reactor which contains active sludge rich in nitrifying bacteria is used in the nitrification step with acid-neutralizing chemicals being added to said reactor if necessary. A high rate denitrification reactor, which contains a very compact biomass which is capable of converting nitrate to nitrogen gas and to which an organic substrate is added, is used in the denitrification step. A method of this type is known from, inter alia, Agrarisch Dagblad of 14 March 1988. With this method the liquid fraction of fermented semi-liquid manure is treated. The biologically degradable organic substances, nitrifiable nitrogen and phosphorus, which are present in the liquid fraction of anaerobic or fermented semi-liquid manure can be largely removed. The method essentially consists in a coupling of a nitrification step in a nitrification reactor in which ammonia is converted by bacteria to oxidized nitrogen with a denitrification step in a denitrification reactor in which oxidized nitrogen is converted by bacteria to nitrogen gas, the phosphate present in the liquid being concentrated as a chemical precipitate in the reactor at the same time. Oxidation of ammonia results in lowering of the pH, which with this method can be countered by metering in lime and/or metering in effluent from the denitrification reactor (recycling) to the nitrification reactor. During the nitrification step of this method there will also be some removal of nitrogen and phosphate by means of nitrogen and phosphate incorporation in the new cells of the active sludge. This nitrogen and phosphate was liberated during the fermentation of the manure whereby degradable substances yield CO.sub.2 and CH.sub.4. With this method the nitrification reactor (which can be either a fed batch reactor or a batch reactor) is operated batchwise. It is then aerated until all ammonia has been nitrified, after which the aeration is stopped temporarily in order to allow the sludge to settle. The nitrified liquid manure is run off for treatment in the denitrification step, while the active sludge remains behind in the nitrification reactor for a subsequent cycle. In the denitrification step the effluent from the nitrification reactor is pumped upwards through a USB (upflow sludge bed) reactor. In this reactor there is a very compact biomass which is capable of converting nitrate to nitrogen gas. In order to allow this step to proceed, an organic substrate--for example methanol--must be added to the reactor. Acid is consumed during the denitrification step, as a result of which the pH in the bacterial bed rises. As a consequence of this rise, an insoluble precipitate of phosphate with the calcium ions present in the liquid forms. The manure processing consisting of manure fermentation and separation of fermented manure, followed by the method for treatment of the liquid fraction of fermented semi-liquid manure, which has been described above, is shown in FIG. 1. (The numerals of this and the following FIGURES are explained in Table A).
A number of manure processing works are being developed at present, for example Promest in Helmond. In these works semi-liquid manure is evaporated to give a dry product, which costs a great deal of energy since semi-liquid manure consists of more than 90% water. Moreover, this evaporation is a complex technology which in fact still has to be developed for use on manure. The cost price of processing of this type for the formation of dry granular or powder manure is consequently very high.
An approach which differs from that described above is the treatment of semi-liquid manure in conventional effluent treatment installations. Currently this is also being used for treatment of liquid manure from calves. The conventional manure treatment has the significant disadvantages that the process produces a large amount of sludge (excess bacteria) and that the process is not capable of removing the phosphate. This means that extra provisions have to be made for sludge treatment and dephosphating. A conventional manure treatment also requires a fairly large amount of space.
This method, as reported in Agrarisch Dagblad of 17 March 1988, has the advantage that it is relatively inexpensive and can be carried out in a compact installation. However, a number of problems also arise in this case in the treatment of fermented manure.
A compact manure treatment installation for manure and fermented manure or Kjeldahl-N containing waste water can be produced and maintained only if:
a) the metering of the fermented liquid fraction is matched to the nitrification capacity of the nitrification reactor. The nitrification reactor must not be overloaded but must also not operate underloaded. PA1 b) The metering of methanol (or other sources of carbon) to the denitrification reactor is matched to the nitrate load in the denitrification reactor. In the case of undermetering not all nitrate is removed; in the case of overmetering, however, methanol (or other source of carbon) is present in the effluent to be discharged. PA1 c) The effluent recycling from denitrification reactor to nitrification reactor is controlled such that it is optimal. Too little recycling leads to a nitrate concentration which has an inhibitory effect on the bacteria; too much recycling has the consequence that the reactor is filled mainly with liquid which has already been treated. PA1 the incoming nitrogen load; PA1 the information from the WAZU respiration meter (described below); PA1 the pH in the nitrification reactor, the criterion for which is that it is in the range limited by 6 and 8.5; PA1 the amount of air required PA1 the residence time PA1 the temperature in both the nitrification reactor and the denitrification reactor, the criterion for which is that this is lower than 40.degree. C.; PA1 the concentration of oxidized nitrogen in the influent for the denitrification reactor, the criterion for which is that the concentration is between 0 and 4 g N/1; PA1 the concentration of oxidized nitrogen in the nitrification reactor, the criterion for which in the sludge/liquid mixture in the reactor is that the concentration is between 0 and 4 g N/1; PA1 the concentration of the carbon source in the effluent from the denitrification reactor; PA1 the gas production in the denitrification reactor. PA1 a nitrification reactor which is provided with aeration, feed of liquid to be treated, feed of acid-neutralizing chemicals, active sludge rich in nitrifying bacteria, sludge discharge, effluent discharge; PA1 a line through which the effluent from the reactor can be fed to the denitrification reactor; PA1 a denitrification reactor which is provided with feed of effluent from the nitrification reactor, feed of a carbon source, an upflow sludge bed (USB) column, a very compact biomass capable of converting nitrate to nitrogen gas, phosphate-rich sludge discharge, effluent discharge, nitrogen gas discharge; PA1 a line through which the effluent from the denitrification reactor can be discharged.
Said points can be achieved by the use of separate instruments, it being necessary to carry out some of the diverse operations by hand. Moreover, the results of the various measurements cannot be integrated and translated into a control action without the intervention of one operator. Furthermore, the effluent from the nitrification reactor can still contain organic substances which cannot be further degraded in the nitrification reactor. Organic material which passes into the denitrification reactor can be converted into inorganic material in that reactor with the liberation of ammonium nitrogen which is then (insofar as it is not fed via the recycle stream) discharged with the effluent.
The aim of a copending European application 90.202728.3 is to eliminate these problems. It relates to a method of the type indicated in the preamble which is characterized in that the loading of the nitrification reactor is controlled and the optimum nitrification and denitrification are obtained on the basis of one or more of the following data:
An aspect of this process may include the use of an instrument, a respiration meter (WAZU respiration meter). Using the respiration meter, the time at which the treatment processes are complete can be established and both the Kjeldahl-N concentration in the liquid fraction of fermented manure to be treated and the nitrate concentration of the effluent from the nitrification reactor (=feed for the denitrification reactor) can be calculated. However, it should be noticed that the use of such a respiration meter is not required. The other data mentioned are also sufficient for a good control of the process. The liquid streams and control lines in relation to the respiration meter are shown schematically in FIG. 2. The respiration meter can control the entire method automatically on the basis of the data collated and calculated by the instrument. However, as already mentioned, such a respiration meter is certainly not necessary.
The nitrification is followed by a denitrification process.
Furthermore, the optimal conditions for the treatment methods have been investigated in both the nitrification and the denitrification reactor. The biomasses in both the nitrification reactor and the denitrification reactor produce heat. Because of the high concentration of biomass and the high rates of conversion which are realized in both reactors, there will be a net excess of heat in both reactors if no measures are taken. It was found in laboratory experiments, that for a nitrifying bacterial population the optimal temperature of this bacterial population is between 31 and 35.degree. C. and that the maximum temperature which can be tolerated is 40.degree. C. On the basis of general scientific information, it can be anticipated that the same temperature limits apply for the denitrifying bacterial population. Thermophilic denitrifying bacteria are known. These operate at temperatures above about 50.degree. C. However, for various reasons it is not desirable to use thermophilic organisms in the denitrification reactor: the effluent to be discharged will be much too warm and the recycle stream to the nitrification reactor may not be too warm. Both the nitrification and the denitrification reactor can be operated only if there is a provision for removal of heat from the respective reactor contents by a suitable means or due to cooling to the air by a suitable design.
For the present method, the conditions in the denitrification reactor must be kept such that phosphate can precipitate. The efficiency of the phosphate removal is dependent on the pH and the HCO.sub.3.sup.- /CO.sub.2.sup.2- ratio in the denitrification reactor.
The desired pH can be obtained by using an organic carbon source for the denitrification reactor with a specific chemical oxygen consumption (COC)/total organic carbon (TOC) ratio in the present method. The fact is that alkalinity (alkali, bicarbonate and carbonate) is produced in the denitrification reactor under the influence of the denitrification reaction. The production of alkalinity is dependent on the COC/TOC ratio of the organic carbon source in the denitrification reaction. Usually methanol is used as an organic carbon source. Methanol has a high COC/TOC ratio and results in a higher production of alkalinity than, for example, glucose, which has a much lower COC/TOC ratio. Experiments have shown that the COC/TOC ratio must be above 3.75.
As stated, the pH falls in the nitrification reactor on the oxidation of the ammonia. To counter acidification of the reactor, an alkali can be metered in or effluent can be recycled from the denitrification reactor to the nitrification reactor. It has been established experimentally that the concentration of oxidized nitrogen in the nitrification reactor in the sludge/liquid mixture is between 0 and 4 g N/1 and preferably is been found that the concentration of oxidized nitrogen in the influent for the denitrification reactor is between 0 and 4 g N/1 and is preferably between 1.0 and 1.4 g N/1. In order to achieve this, the effluent from the denitrification reactor can be of oxidized nitrogen at the feed location in the reactor. Furthermore, this recycling is intended to obtain a higher stream velocity in the denitrification reactor, which promotes the contact between biomass and substrate in the reactor. Recycling can take place directly from effluent stream to influent stream for the denitrification reactor. It is, however, also possible (and in fact better for the overall process) for recycling of effluent from the denitrification reactor to be used, this recycling taking place entirely or partially via the nitrification reactor. The aim of this is then to achieve both a saving in the chemicals consumption for pH control in the nitrification reactor and to achieve a dilution of the reactor contents of the nitrification reactor such that the content of oxidized nitrogen is always lower than 4 g N/1.
Another aspect is the use of a separation step, e.g. a physical/chemical flocculation step and a floccule separator or a membrane technology after the nitrification step. The purpose of said separation previous to the denitrification reactor is catching suspended and colloidally dissolved organic substances, that otherwise would mineralize in the denitrification reactor resulting in the formation of ammonia nitrogen. A physical/chemical flocculation step plus floccule separation is shown schematically in FIG. 3. The residual organic substance can be removed from the effluent with the aid of flocculating adjuvants and a process for separation of the flocculent from the effluent. By positioning the separation upstream of the denitrification step, the organic substances can be removed before they are converted to inorganic substances and ammonium nitrogen is formed. A further advantage of this is that the carbonate content in the effluent from the nitrification reactor is low (lower than in the effluent from the denitrification) reactor, to which organic substrate is added). This is advantageous if a flocculating adjuvant is used which forms a precipitate with carbonate. If a flocculating adjuvant is used which contains cations which precipitate with phosphate, an additional phosphate removal is performed.
The copending application also relates to an installation which is suitable for carrying out the method as described above, comprising:
In the most simple form, the installation (shown schematically in FIG. 2) consists of the combination of a batch reactor (to which all influent (7) is added at once per cycle) or a fed batch reactor (to which the influent is added gradually or stepwise per cycle) as nitrification reactor (9) and a continuously fed upflow sludge bed (USB) reactor as denitrification reactor (13). The two reactors are operated connected in series, without bypass of the nitrification reactor (9) but optionally with backmixing (33) from the denitrification reactor (13) to the nitrification reactor (9).
The use of the WAZU respiration meter (18) (described below), a measurement and control unit with which the course of the respiration rate of the biomass in the reactor (9) is followed, is characteristic of the installation according to the copending application.
The nitrification reactor (9) of the apparatus is provided with aeration (10), a feed of liquid (7) to be treated, a sludge discharge (11), effluent discharge and optionally a feed of effluent from the denitrification reactor (33), all of which are controlled by the WAZU respiration meter (18) (Netherlands Patent Application 86.00396, filed on 6 February 1986). This respiration meter also controls the metering of the source of carbon (14) for the denitrification reactor (13). This denitrification reactor is additionally provided with nitrogen gas discharge (17) and effluent recirculation (33) or discharge (16) (see FIGS. 2 and 5).
Another embodiment of the installation according to the copending application (shown schematically in FIG. 4) is also provided with a line (32) through which the effluent from the denitrification reactor (13) can be partially recycled to the effluent (12) from the nitrification reactor (9) which serves as influent for the denitrification reactor (13) and additionally this installation is provided with a feed of one or more acid-neutralizing chemicals (8) to the nitrification reactor (9).
Furthermore, the apparatus can comprise a combination of the two above installations (FIGS. 4 and 5), i.e. an installation as shown in FIG. 6, this installation being provided with lines through which the effluent (16) from the denitrification reactor (13) can be partially recycled (lines 33 and 32 respectively) to the nitrification reactor (9) and to the effluent (12) from the nitrification reactor (9) which serves as influent for the denitrification reactor (13).
The three last mentioned installations, shown in FIGS. 4, 5 and 6, can comprise a further addition (see FIG. 7) in the form of a feed of chemicals for phosphate precipitation (20).
Furthermore, all of these installations (shown in FIGS. 4, 5, 6 and 7) can be provided with one or more separation or flocculation installations (19). The flocculation installation as such is shown schematically in FIG. 3.
The apparatus according to the copending application which have already been described can be provided with the flocculation installations at various locations (FIGS. 8, 9 and 10). In the installation according to FIG. 8, the flocculation installation (19) is positioned in such a way that the effluent (16) from the denitrification reactor (13) flows through the flocculation installation (19 and FIG. 3) upstream of the recycle (34,35) or discharge (22).
In the installation according to FIG. 9, the flocculation installation (19) is positioned in such a way that only the effluent (16) from the denitrification reactor (13) which is to be discharged flows through the flocculation installation (19).
In the installation according to FIG. 10, which is preferred, the flocculation installation (19) is positioned in such a way that the effluent (12) originating from the nitrification reactor (9) flows through the flocculation installation (19) before it flows into the denitrification reactor (13).
The apparatus according to the copending application in which the nitrification reactor is provided with feed of the effluent (33,34) from the denitrification reactor (13) can be provided with a spray installation (25 in FIG. 10) through which the effluent (33 or 34) from the denitrification reactor (13) can be sprayed into the nitrification reactor (9) to prevent foam formation.
Furthermore, all installations according to the copending application can be provided with one or more buffer tanks (23) (FIG. 10).
In the above process, all effluent (12) from the nitrification reactor passes through the separator (19), this means a high load for the separator.